Hi,

My 2006 A4 with 75k miles has been shuddering when I come to a stop occasionally for a few months and on the bad times, the power has given out and the car died (it restarts right away). I've had it looked at but no one found a problem.
Today while driving on the highway with the AC on, I noticed gray smoke coming from what seemed to be the back of the car. Fast forward to getting home (I was close to home and drove slowly) and it is leaking oil from the front undercarriage, it sounds like metal is grating in the back of the car, the shuddering is terrible, the car is revving on its own (from 1.5 RPMs to 2) and when I first shut the car down, there was a bad smell of burning rubber inside the car. Also, when I turned off the AC after noticing the smoke and leaking, the smoke stopped.
Any thoughts?

Thanks!